I might be wrong but it sounds like your carbon might be a little bendy under hard stroke shots. If that's the case then you'll get unexpected results on hard stroked shots. I don't think it possible to reduce squirt to the point that you can't hard stroke your way out of making a shot.
I have two Schon's now, and 2 Jacoby Ultra wood shafts, and one Jacoby 12.7 carbon for them. First bought a Jacoby Ultra when I had my 1st Schon and really liked it. When my wife stole that Schon from me and told me to buy another, I was going to order another Ultra right away, but had a chance to try out their carbon shaft out at a state tournament and ordered that in a 12.7mm as it matched up with the ultra wood, instead. After getting the carbon shaft and playing with it for a few weeks, I ordered another Ultra wood shaft. I just had a hard time adjusting to it. The hit was very similar once the tip broke in, seemed to have a little more action with the carbon, incredibly smooth and slick with the carbon, yet I just was not adjusting to it. I have let 3 other players play some with my Jacoby carbon and they absolutely love it, so it's probably just me and I still do practice with it now and then and sometimes play great, and sometimes the ball takes off line for me. I'm sure it's just lack of concertation on my part. It also seems like a lighter feeling in the front than the Ultra wood shaft. I really like the Ultra wood shaft, although it has a much different hit than a stock Shon shaft. Just for grins awhile back, I turned a stock Schon shaft down to 12.6mm at the tip, but left a fairly fast taper on it similar to the stock shaft. Even though the tip is smaller, the shaft actually feels better in my hand than the Ultra as it's actually a little fatter about 6 to 8" back from the tip. I really like this stock shaft as it gives a great feedback, and just is pleasing to shoot. I do shoot better with the Ultra shaft though, but could be because thats what I am most used to, and the Ultra shaft has less deflection than the Schon. Also as to the hit on a Ultra, I am using Ultraskin Fire medium tips and like that tip alot, tried the black softs, but like the Fire mediums better. May try a black medium at some point on one of the two shafts to compare.